1. Technical Field of the Invention
This invention relates generally to a pressure applying device for resistance welding, and more particularly to a pressure applying device for use in welding robots.
2. Prior Art
In order to provide better operability in welding process with minimized influences due to inertia force, the pressure applying devices for welding robots are required to be constructed into a smaller and lighter device. However, to achieve good resistance welding results, it is desired that greater welding force by electrode tips acts on the parts to be welded at the time of welding.
In conventional welding pressure applying devices, some attempts were made for improvement. For example, the selection of aluminum alloy having a small specific gravity for a gun arm material, or the forming of ribs on the arm for reinforcement purpose, or the use of a reinforcement material for a lightweight device with great stiffness.
However, the gun arm of the welding pressure applying device has a complicated shape, and it is inevitable to use iron castings generally with low stiffness. Even with the above improvement, a hinge portion of the device, especially of the X-type device, which includes a pin, a pin hole, a bushing, etc., and acts as a supporting point when welding pressure is applied, often experiences a remarkable wear because great force is repeatedly applied. And, the supporting means of the conventional device often exhibits a mechanical play which may cause misalignment between the ends of paired electrode tips, resulting in a poor welding accuracy and a shortened life of the device.